1 //===---- llvm-jitlink-elf.cpp -- ELF parsing support for llvm-jitlink ----===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // ELF parsing support for llvm-jitlink.
10 //
11 //===----------------------------------------------------------------------===//
12
13 #include "llvm-jitlink.h"
14
15 #include "llvm/Support/Error.h"
16 #include "llvm/Support/Path.h"
17
18 #define DEBUG_TYPE "llvm_jitlink"
19
20 using namespace llvm;
21 using namespace llvm::jitlink;
22
isELFGOTSection(Section & S)23 static bool isELFGOTSection(Section &S) { return S.getName() == "$__GOT"; }
24
isELFStubsSection(Section & S)25 static bool isELFStubsSection(Section &S) { return S.getName() == "$__STUBS"; }
26
getFirstRelocationEdge(LinkGraph & G,Block & B)27 static Expected<Edge &> getFirstRelocationEdge(LinkGraph &G, Block &B) {
28 auto EItr = std::find_if(B.edges().begin(), B.edges().end(),
29 [](Edge &E) { return E.isRelocation(); });
30 if (EItr == B.edges().end())
31 return make_error<StringError>("GOT entry in " + G.getName() + ", \"" +
32 B.getSection().getName() +
33 "\" has no relocations",
34 inconvertibleErrorCode());
35 return *EItr;
36 }
37
getELFGOTTarget(LinkGraph & G,Block & B)38 static Expected<Symbol &> getELFGOTTarget(LinkGraph &G, Block &B) {
39 auto E = getFirstRelocationEdge(G, B);
40 if (!E)
41 return E.takeError();
42 auto &TargetSym = E->getTarget();
43 if (!TargetSym.hasName())
44 return make_error<StringError>(
45 "GOT entry in " + G.getName() + ", \"" +
46 TargetSym.getBlock().getSection().getName() +
47 "\" points to anonymous "
48 "symbol",
49 inconvertibleErrorCode());
50 return TargetSym;
51 }
52
getELFStubTarget(LinkGraph & G,Block & B)53 static Expected<Symbol &> getELFStubTarget(LinkGraph &G, Block &B) {
54 auto E = getFirstRelocationEdge(G, B);
55 if (!E)
56 return E.takeError();
57 auto &GOTSym = E->getTarget();
58 if (!GOTSym.isDefined() || !isELFGOTSection(GOTSym.getBlock().getSection()))
59 return make_error<StringError>(
60 "Stubs entry in " + G.getName() + ", \"" +
61 GOTSym.getBlock().getSection().getName() +
62 "\" does not point to GOT entry",
63 inconvertibleErrorCode());
64 return getELFGOTTarget(G, GOTSym.getBlock());
65 }
66
67 namespace llvm {
68
registerELFGraphInfo(Session & S,LinkGraph & G)69 Error registerELFGraphInfo(Session &S, LinkGraph &G) {
70 auto FileName = sys::path::filename(G.getName());
71 if (S.FileInfos.count(FileName)) {
72 return make_error<StringError>("When -check is passed, file names must be "
73 "distinct (duplicate: \"" +
74 FileName + "\")",
75 inconvertibleErrorCode());
76 }
77
78 auto &FileInfo = S.FileInfos[FileName];
79 LLVM_DEBUG({
80 dbgs() << "Registering ELF file info for \"" << FileName << "\"\n";
81 });
82 for (auto &Sec : G.sections()) {
83 LLVM_DEBUG({
84 dbgs() << " Section \"" << Sec.getName() << "\": "
85 << (llvm::empty(Sec.symbols()) ? "empty. skipping."
86 : "processing...")
87 << "\n";
88 });
89
90 // Skip empty sections.
91 if (llvm::empty(Sec.symbols()))
92 continue;
93
94 if (FileInfo.SectionInfos.count(Sec.getName()))
95 return make_error<StringError>("Encountered duplicate section name \"" +
96 Sec.getName() + "\" in \"" + FileName +
97 "\"",
98 inconvertibleErrorCode());
99
100 bool isGOTSection = isELFGOTSection(Sec);
101 bool isStubsSection = isELFStubsSection(Sec);
102
103 bool SectionContainsContent = false;
104 bool SectionContainsZeroFill = false;
105
106 auto *FirstSym = *Sec.symbols().begin();
107 auto *LastSym = FirstSym;
108 for (auto *Sym : Sec.symbols()) {
109 if (Sym->getAddress() < FirstSym->getAddress())
110 FirstSym = Sym;
111 if (Sym->getAddress() > LastSym->getAddress())
112 LastSym = Sym;
113
114 if (isGOTSection) {
115 if (Sym->isSymbolZeroFill())
116 return make_error<StringError>("zero-fill atom in GOT section",
117 inconvertibleErrorCode());
118
119 // If this is a GOT symbol with size (i.e. not the GOT start symbol)
120 // then add it to the GOT entry info table.
121 if (Sym->getSize() != 0) {
122 if (auto TS = getELFGOTTarget(G, Sym->getBlock()))
123 FileInfo.GOTEntryInfos[TS->getName()] = {Sym->getSymbolContent(),
124 Sym->getAddress()};
125 else
126 return TS.takeError();
127 }
128 SectionContainsContent = true;
129 } else if (isStubsSection) {
130 if (Sym->isSymbolZeroFill())
131 return make_error<StringError>("zero-fill atom in Stub section",
132 inconvertibleErrorCode());
133
134 if (auto TS = getELFStubTarget(G, Sym->getBlock()))
135 FileInfo.StubInfos[TS->getName()] = {Sym->getSymbolContent(),
136 Sym->getAddress()};
137 else
138 return TS.takeError();
139 SectionContainsContent = true;
140 }
141
142 if (Sym->hasName()) {
143 if (Sym->isSymbolZeroFill()) {
144 S.SymbolInfos[Sym->getName()] = {Sym->getSize(), Sym->getAddress()};
145 SectionContainsZeroFill = true;
146 } else {
147 S.SymbolInfos[Sym->getName()] = {Sym->getSymbolContent(),
148 Sym->getAddress()};
149 SectionContainsContent = true;
150 }
151 }
152 }
153
154 JITTargetAddress SecAddr = FirstSym->getAddress();
155 uint64_t SecSize =
156 (LastSym->getBlock().getAddress() + LastSym->getBlock().getSize()) -
157 SecAddr;
158
159 if (SectionContainsZeroFill && SectionContainsContent)
160 return make_error<StringError>("Mixed zero-fill and content sections not "
161 "supported yet",
162 inconvertibleErrorCode());
163 if (SectionContainsZeroFill)
164 FileInfo.SectionInfos[Sec.getName()] = {SecSize, SecAddr};
165 else
166 FileInfo.SectionInfos[Sec.getName()] = {
167 ArrayRef<char>(FirstSym->getBlock().getContent().data(), SecSize),
168 SecAddr};
169 }
170
171 return Error::success();
172 }
173
174 } // end namespace llvm
175